CVE-2001-0865 in IOS
Summary
by MITRE
Cisco 12000 with IOS 12.0 and line cards based on Engine 2 does not support the "fragment" keyword in an outgoing ACL, which could allow fragmented packets in violation of the intended access.
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Analysis
by VulDB Data Team • 05/19/2019
The vulnerability identified as CVE-2001-0865 affects Cisco 12000 series routers operating with IOS version 12.0 and utilizing line cards based on the Engine 2 architecture. This represents a significant security flaw in the router's access control implementation that directly impacts network traffic filtering capabilities. The issue stems from the absence of proper support for the "fragment" keyword within outgoing access control lists, creating a critical gap in the router's ability to enforce comprehensive packet filtering policies. This weakness allows fragmented packets to bypass intended access restrictions, potentially enabling malicious actors to circumvent security controls that were designed to block specific traffic patterns.
The technical flaw manifests in the router's inability to properly process and evaluate fragmented packets when they encounter outgoing access control lists. When a router receives a fragmented packet, it must reassemble the fragments before applying access control rules to ensure proper filtering decisions. However, the affected Cisco 12000 series routers with Engine 2 line cards fail to implement this critical reassembly process for outgoing traffic, resulting in fragmented packets being permitted through access control lists without proper evaluation of their contents. This vulnerability directly relates to CWE-119, which addresses improper restriction of operations within a limited access scope, and CWE-295, which deals with improper certificate validation. The flaw essentially creates a bypass mechanism that allows attackers to exploit the router's filtering capabilities by sending fragmented packets that would normally be blocked by ACL rules.
The operational impact of this vulnerability extends beyond simple access control bypass, as it fundamentally undermines the security posture of networks relying on these Cisco 12000 routers for traffic filtering and access control. Network administrators who implement outgoing ACLs expecting to block specific traffic patterns may find their security policies ineffective against fragmented packet attacks, potentially allowing malicious traffic to traverse the network. This vulnerability creates opportunities for attackers to exploit network segments that should be protected by access control lists, particularly when dealing with protocols that commonly generate fragmented packets such as ICMP, UDP, or TCP traffic. The attack surface is further expanded when considering that fragmented packets can carry malicious payloads that would normally be blocked by traditional access control mechanisms, effectively creating a backdoor for unauthorized network access.
The security implications of this vulnerability align with several ATT&CK framework techniques including T1071.004 for Application Layer Protocol: DNS and T1566 for Phishing with Spoofed Credentials, as attackers could leverage fragmented packets to bypass network controls and deliver malicious payloads. Organizations implementing these routers in critical network segments face potential exposure to various attack vectors that exploit the fundamental flaw in packet processing and access control enforcement. The vulnerability also relates to T1133 for External Remote Services and T1046 for Network Service Scanning, as attackers could use fragmented packets to probe network services and bypass access restrictions that should prevent such activities. Mitigation strategies should include immediate firmware upgrades to versions that properly support the fragment keyword in outgoing ACLs, implementation of additional network monitoring to detect anomalous fragmented packet behavior, and careful review of existing access control policies to ensure they account for this vulnerability. Network administrators should also consider implementing redundant security controls and monitoring solutions that can detect and prevent the exploitation of this specific weakness in the router's packet filtering implementation.